[Prior Art]
it has been widely known that the directional stability of a motor vehicle is lost in some cases, depending on the conditions of the road surface, if the wheels of the motor vehicle are locked when the brake is applied sharply. Therefore, it is in practice to control the braking force in such a manner as to eventually keep the slip factor of the wheels at approximately 20%, that is, so as to obtain the maximum coefficient of friction, by controlling the brake fluid pressure in accordance with the changes in the wheel velocity and the wheel acceleration, in consideration of the fact that the wheel velocity declines abruptly immediately before the coefficient of friction .mu. attains the maximum value in relation to the wheels when the pressure of the brake fluid working on the wheel cylinder is increased at the time of braking. Specifically, motor vehicles are equipped with an anti-skid control system which controls the braking force by reducing, increasing, or maintaining the pressure of the brake fluid working on the wheel cylinders, so that the wheels are not locked at the time of sharp braking.
With respect to such an anti-skid control system, the Japanese Kokai No. 155163-1987, for example, proposes an anti-skid control process which consists in finding a simulated vehicle speed on the basis of the wheel velocity, working out by arithmetic operations a standard speed which follows up this simulated vehicle speed at a speed lower by a certain fixed speed difference, and increasing the brake fluid pressure only in case this high peak speed based on the simulated vehicle speed is either equal to or higher than the standard speed but again reducing the brake fluid pressure in case the high peak speed is lower than the standard speed, so that the process serves the purpose of preventing a wheel lock at an early point in time in consequence of the failure in the recovery of the vehicle speed in case the vehicle speed is low.